Cooling system

ABSTRACT

A cooling system includes: a compressor; a condenser; an expansion valve; an evaporator; an internal heat exchanger having a first conduit in heat exchanging contact with a second conduit, the first conduit being part of a high pressure fluid line between the condenser and the expansion valve, the second conduit being part of a low pressure fluid line between the evaporator and the compressor; a bypass line connecting the high pressure fluid line with the low pressure fluid line and for injecting small amounts of liquid fluid from the high pressure fluid line into the low pressure fluid line; a valve arranged in the bypass line for opening and closing the bypass line; and a control device for monitoring a load point of the compressor and controlling the valve to an open position when the load point exceeds a threshold.

CROSS-REFERENCE TO PRIOR APPLICATIONS

This application is a U.S. National Phase application under 35 U.S.C. § 371 of International Application No. PCT/EP2017/062965, filed on May 30, 2017, and claims benefit to British Patent Application No. GB 1609498.9, filed on May 31, 2016. The International Application was published in English on Dec. 7, 2017 as WO 2017/207526 under PCT Article 21(2).

FIELD

The invention relates to a cooling system comprising, connected in a loop by fluid lines and in succession, a compressor, a condenser, an expansion valve and an evaporator, further comprising an internal heat exchanger having a first conduit in heat exchanging contact with a second conduit, wherein the first conduit is part of the high pressure fluid line between the condenser and the expansion valve and wherein the second conduit is part of the low pressure fluid line between the evaporator and the compressor.

BACKGROUND

Such a cooling system is for example known from EP 1043550. This publication describes a cooling system in which a fluid, in particular CO2 is used, which is made super-critical in the high pressure line between the compressor and the expansion valve. The internal heat exchanger cools the fluid in the high pressure line, such that the COP (coefficient of performance) of the cooling system is improved.

During high load points, typically at high condensation temperature with a low pressure on the suction side of the compressor, the vapor in the low pressure fluid line could be superheated too much. This effect is partially contributed to the internal heat exchanger, which transfers heat from the high pressure fluid line to the low pressure fluid line.

So, although the internal heat exchanger has the advantage of improving the COP during most of the operation conditions of the cooling system, in high load point conditions, the internal heat exchanger result in a disadvantage, because the fluid in the low pressure fluid line could get too much superheated. This results in a decrease of the volumetric efficiency of the compressor, which in turn results in a decreased COP. It also results in a too high compressor outlet temperature, which has negative effects on for example the oil, and it could lead to overheating of the compressor itself.

SUMMARY

In an embodiment, the present invention provides a cooling system, comprising: connected in a loop in succession, a compressor; a condenser; an expansion valve; and an evaporator; an internal heat exchanger having a first conduit in heat exchanging contact with a second conduit, the first conduit being part of a high pressure fluid line between the condenser and the expansion valve, the second conduit being part of a low pressure fluid line between the evaporator and the compressor; a bypass line connecting the high pressure fluid line with the low pressure fluid line and being configured to inject small amounts of liquid fluid from the high pressure fluid line into the low pressure fluid line; a valve arranged in the bypass line and configured to open and close the bypass line; and a control device configured to monitor a load point of the compressor and to control the valve to an open position when the load point exceeds a threshold.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described in even greater detail below based on the exemplary figures. The invention is not limited to the exemplary embodiments. Other features and advantages of various embodiments of the present invention will become apparent by reading the following detailed description with reference to the attached drawings which illustrate the following:

FIG. 1 shows a schematic view of a first embodiment of a cooling system according to the invention.

FIG. 2 shows a schematic view of a second embodiment of a cooling system according to the invention.

DETAILED DESCRIPTION

In an embodiment, the present invention provides a cooling system, which is characterized by a bypass line connecting the high pressure fluid line with the low pressure fluid line for injecting small amounts of liquid fluid from the high pressure fluid line into the low pressure fluid line; and

a valve arranged in the bypass line for opening or closing the bypass line; and a control device for monitoring the load point of the compressor and for controlling the valve to an open position when the load point exceeds a threshold.

With the cooling system according to the invention, the load point of the compressor is monitored and when the load point becomes too high, which would result in too much superheated vapor in the low pressure fluid line, the valve is controlled open for a short time, such that a small amount of fluid from the high pressure fluid line is injected into the low pressure fluid line. The fluid in the high pressure fluid line is liquid and upon injection in the low pressure fluid line, the liquid fluid will evaporate resulting in a cool down of the superheated vapor in the low pressure fluid line.

As soon as the vapor is cooled down and the load point is below the threshold, the valve is controlled to close the bypass line, such that the cooling system can operate in the common way.

In a preferred embodiment of the cooling system according to the invention the bypass line is arranged in the internal heat exchanger between the first conduit and the second conduit.

By arranging the bypass line in the internal heat exchanger, it is more easy to convert existing layouts to a cooling system according to the invention. It would only require to exchange the internal heat exchanger of an existing cooling system with an internal heat exchanger incorporating a bypass line to convert an existing cooling system to a cooling system according to the invention.

The position of the bypass line in the internal heat exchanger could be chosen depending on the conditions, for example at the beginning, the middle or the end of the internal heat exchanger in view of the liquid side.

A further embodiment of the cooling system according to the invention further comprises a temperature sensor and/or a pressure sensor connected to the control device and arranged in the low pressure fluid line, preferably near the compressor.

Whether the vapor in the low pressure fluid line is too much superheated can be derived from the temperature of the fluid in the low pressure fluid line or the pressure thereof. Also a combination of temperature and pressure can be used to determine whether the vapor is too much superheated and the valve needs to be controlled open to cool the vapor down.

In another embodiment of the cooling system according to the invention the valve is a back pressure valve or a thermostat valve having the respective sensor in fluid connection with the low pressure fluid line. These valves provide mechanical a control device, wherein the superheated condition is mechanically detected and the valve is opened when the pressure exceeds a threshold or the temperature causes a bi-metal to open the valve.

Depending on the general conditions in the internal heat exchanger, the valve and control device could also be embodied as a small hole. The flow through this hole will only be considerate, when the pressure difference between the first and second conduit. So, by designing the dimensions of this hole, the same effect as a back pressure valve could be obtained.

The invention also relates to a method for controlling a cooling system according to the invention, which method comprises the steps:

while having the bypass line closed, monitoring the load point of the compressor;

when the monitored load point exceeds a threshold, shortly opening the bypass line by controlling the valve, to inject an amount of liquid from the high pressure fluid line into the low pressure fluid line.

In a preferred embodiment of the method according to the invention the load point of the compressor is monitored by the temperature of the fluid entering the compressor.

This temperature is measured for example in the low pressure fluid line just before the fluid enters the compressor. This provides a reliable value to determine whether the overheated vapor should be cooled down by injection of liquid fluid from the high pressure fluid line.

In yet another embodiment of the method according to the invention the load point of the compressor is monitored by the pressure of the fluid entering the compressor.

FIG. 1 shows a first embodiment of a cooling system 1 according to the invention. The cooling system 1 has connected in a loop by fluid lines and in succession, a compressor 2, a condenser 3, an expansion valve 4 and an evaporator 5. To further improve the efficiency of the cooling system 1 an internal heat exchanger 6 is provided with a first conduit 7 arranged in the high pressure fluid line 8, 9 between the condenser 3 and the expansion valve 4. The internal heat exchanger 6 has a second conduit 10 in heat exchanging contact with the first conduit 7, and arranged in the low pressure fluid line 11, 12 between the evaporator 5 and the compressor 2.

A bypass line 13 with a valve 14 is provided between the high pressure line 8 and the low pressure line 12. A temperature sensor 15 is furthermore provided in the low pressure fluid line 12 to detect the temperature of the vapor. The temperature sensor 15 is connected to the controller 16, which can control the valve 14 open or closed.

The controller 16 thus checks whether the temperature measured by the temperature sensor 15 exceeds a threshold and then controls the valve 14 to an open state, such that liquid fluid can flow from the high pressure line 8 via the bypass line 13 to the low pressure line 12 to cool down the vapor in the low pressure line.

FIG. 2 shows schematically a second embodiment 20 of a cooling system according to the invention. The cooling system 20 has schematically, a compressor 21, a condenser 22, a restriction 23 and an evaporator 24.

An internal heat exchanger 25 is provided having an internal channel 26 and an concentrically arranged external channel 27. The external channel provides the high pressure fluid line and connects the condenser 22 with the restriction 23, while the internal channel 26 connects the evaporator 24 with the compressor 21 and provides the low pressure fluid line.

Due to the concentric arrangement of the internal channel 26 and the external channel 27 heat can be exchanged between the high pressure fluid line and the low pressure fluid line.

Furthermore, a valve 28 is provided between the wall of the internal channel 26 and the external channel 27. This valve 28 is operated by an actuator 29, which can be triggered by the temperature or the pressure in the low pressure fluid line.

When the valve 28 is opened, liquid fluid can flow from the high pressure fluid line to the low pressure fluid line to cool the vapor in the low pressure fluid line.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. It will be understood that changes and modifications may be made by those of ordinary skill within the scope of the following claims. In particular, the present invention covers further embodiments with any combination of features from different embodiments described above and below. Additionally, statements made herein characterizing the invention refer to an embodiment of the invention and not necessarily all embodiments.

The terms used in the claims should be construed to have the broadest reasonable interpretation consistent with the foregoing description. For example, the use of the article “a” or “the” in introducing an element should not be interpreted as being exclusive of a plurality of elements. Likewise, the recitation of “or” should be interpreted as being inclusive, such that the recitation of “A or B” is not exclusive of “A and B,” unless it is clear from the context or the foregoing description that only one of A and B is intended. Further, the recitation of “at least one of A, B and C” should be interpreted as one or more of a group of elements consisting of A, B and C, and should not be interpreted as requiring at least one of each of the listed elements A, B and C, regardless of whether A, B and C are related as categories or otherwise. Moreover, the recitation of “A, B and/or C” or “at least one of A, B or C” should be interpreted as including any singular entity from the listed elements, e.g., A, any subset from the listed elements, e.g., A and B, or the entire list of elements A, B and C. 

1. A cooling system, comprising: connected in a loop in succession, a compressor; a condenser; an expansion valve; and an evaporator; an internal heat exchanger having a first conduit in heat exchanging contact with a second conduit, the first conduit being part of a high pressure fluid line between the condenser and the expansion valve, the second conduit being part of a low pressure fluid line between the evaporator and the compressor; a bypass line connecting the high pressure fluid line with the low pressure fluid line and being configured to inject small amounts of liquid fluid from the high pressure fluid line into the low pressure fluid line; a valve arranged in the bypass line and configured to open and close the bypass line; and a control device configured to monitor a load point of the compressor and to control the valve to an open position when the load point exceeds a threshold.
 2. The cooling system according to claim 1, wherein the bypass line is arranged in the internal heat exchanger between the first conduit and the second conduit.
 3. The cooling system according to claim 1, further comprising a temperature sensor and/or a pressure sensor connected to the control device and arranged in the low pressure fluid line.
 4. The cooling system according to claim 1, wherein the valve comprises a back pressure valve or a thermostat valve having the respective sensor in fluid connection with the low pressure fluid line.
 5. A method for controlling the cooling system according to claim 1, which method comprises: while having the bypass line closed, monitoring the load point of the compressor; and when the monitored load point exceeds a threshold, shortly opening the bypass line by controlling the valve, to inject an amount of liquid from the high pressure fluid line into the low pressure fluid line.
 6. The method according to claim 5, wherein the load point of the compressor is monitored by a temperature of a fluid entering the compressor.
 7. The method according to claim 5, wherein the load point of the compressor is monitored by a pressure of a fluid entering the compressor.
 8. The cooling system according to claim 3, wherein the temperature sensor and/or pressure sensor is arranged in the low pressure fluid line near the compressor.
 9. The method according to claim 6, wherein the load point of the compressor is monitored by a pressure of the fluid entering the compressor. 